The XS, TX and RDs were parts bin bikes-many many XS650 parts and RD350/400 parts will work and don't forget the TX500 has the exact engine. You just have find the time to cross reference. Besides nwcp, speedandsport.com has a lot of parts but you really need to know the part number with them. Also try hvccycle.com I have really good luck with them, they sell RD stuff but it crosses over. Make sure all the cams and valves are adjusted to spec with this engine or you will suffer performance wise.